Week 9 - MOLECULAR DEVELOPMENT Part V: Stem cells And regeneration Flashcards
(24 cards)
What defines a stem cell?
Ability to self-renew and differentiate.
After division, a daughter cell can either:
Stay a stem cell.
Start to differentiate.
Potency describes their potential:
Tissue-specific stem cells → Multipotent (specific tissues).
Embryonic stem cells → Pluripotent (all body tissues).
Depletion of stem cells may occur during aging.
What happens as stem cells differentiate?
Stem cells produce transit amplifying cells (progenitors).
These cells:
Divide a few times.
Then produce fully differentiated daughter cells.
How does potency classify stem cells?
Totipotent: Can make all embryonic and extra-embryonic tissues.
Pluripotent: Can become any body tissue (embryonic stem cells).
Multipotent: Can form multiple related cell types (adult stem cells).
Where do embryonic stem cells originate?
From the Inner Cell Mass (ICM) of the blastocyst.
Remain pluripotent by expressing key genes like Oct4, Sox2, Nanog.
Which signals maintain pluripotency in embryonic stem cells?
Oct4, Sox2, Nanog are critical transcription factors.
Oct4/Sox2:
Regulate their own expression.
Regulate Nanog.
Nanog:
Regulates its own expression.
Maintains Oct4/Sox2.
Together they keep cells pluripotent.
What defines the adult stem cell niche, and how does it function?
Adult tissues like skin, blood, intestines, and brain contain multipotent stem cells.
These stem cells:
Undergo continuous self-renewal.
Differentiate into specialized daughter cells to replace damaged or lost cells.
The niche provides a microenvironment that controls:
Stem cell renewal (keeps them undifferentiated).
Survival (protection from stress and apoptosis).
Differentiation (occurs when cells move away from niche signals).
How does the stem cell niche control stem cells?
Mechanical factors:
Adhesion between cells.
Cell density.
Chemical factors:
Local signals (paracrine, endocrine, juxtacrine).
Close to the niche = more “stemness”.
Farther away = cells start differentiating.
Where are adult stem cell niches located in humans?
Bone marrow: Hematopoietic stem cells (blood cells).
Skin: Epidermal stem cells (for wound healing).
Intestinal crypts: Intestinal stem cells (for gut lining renewal).
Brain: Neural stem cells (for limited brain repair).
Muscle: Satellite cells (for muscle regeneration).
These niches provide chemical and mechanical cues to maintain stem cells’ undifferentiated state.
How does the intestinal stem cell niche work?
The small intestine surface is organized into:
Villi: Finger-like projections for nutrient absorption.
Crypts: Invaginations at the base where stem cells reside.
Only crypt cells divide.
Intestinal stem cells at crypt base:
Express Lgr5 (a G-protein coupled receptor marker).
Continuously divide and differentiate as they migrate up the villus.
Entire gut epithelium is replaced every 2–3 days.
Differentiation happens progressively as cells move away from the niche (crypt base).
What does lineage tracing reveal about Lgr5+ cells?
A single Lgr5+ stem cell can regenerate an entire intestinal villus.
Proves that Lgr5+ cells are true multipotent stem cells.
Lineage tracing technique:
Genetically mark one cell.
Track all daughter cells it produces over time.
What is the role of Paneth cells in the gut stem cell niche?
Paneth cells are specialized secretory cells found in the crypts.
Functions:
Secrete antimicrobial peptides for gut immunity.
Provide critical growth factors like Wnt3a to maintain stem cell proliferation.
If Paneth cells are removed:
Stem cells cannot maintain their undifferentiated state properly.
BMP signals from underlying stromal cells promote stem cell differentiation.
Stem cell niche = Paneth cells + supportive signals.
How can a “minigut” be grown from one stem cell?
A single Lgr5+ intestinal stem cell in culture can form:
A miniature gut structure (called an organoid).
This multipotent stem cell:
Self-organizes.
Creates Paneth cells to form its own micro-niche.
Represents a powerful system for studying gut biology and regeneration outside the body.
How are stem cells used to study development and disease?
Study normal development:
Understand how tissues and organs form from stem cells.
Model diseases:
Derive cells from patients with genetic mutations.
Grow them into tissues to observe disease mechanisms.
Drug screening:
Test therapeutic drugs on patient-derived cells before clinical use.
Therapy:
Replace damaged or diseased tissues with lab-grown healthy cells.
Key advantage: Patient-specific cells reduce chances of immune rejection.
What are the origins of embryonic stem cells (ESCs)?
ESCs are derived from:
Inner Cell Mass (ICM) of the blastocyst.
Embryonic Germ Cells (EGCs) — precursor cells that haven’t become sperm or eggs yet.
Key pluripotency genes expressed:
Oct4, Sox2, Nanog — maintain stemness.
Two types of ESCs:
Naïve ESCs: Most immature, maximum pluripotency.
Primed ESCs: Slightly more developed, ready for differentiation into specific lineages.
How are human ESCs grown and induced to differentiate in labs?
Goal: Turn ESCs into specific cell types (e.g., neurons, cardiomyocytes).
Critical factors:
Discover and apply the right inducing signals (growth factors, chemicals).
Modify culture conditions — the size, shape, and mechanical properties of growth environment impact differentiation.
Differentiation protocols carefully control external signals.
How are stem cells supported in culture for therapeutic or research purposes?
ESCs are grown on a feeder layer of irradiated embryonic fibroblast cells.
Feeder cells:
Provide growth factors.
Offer extracellular matrix for physical support.
Facilitate direct cell-cell interactions to maintain pluripotency.
Ethical concerns exist regarding ESC use (destruction of embryos).
Research often turns to iPSCs as an alternative.
What are induced pluripotent stem cells (iPSCs) and how are they created?
iPSCs are adult somatic cells reprogrammed back to pluripotency.
Takahashi and Yamanaka (2006) landmark discovery:
Introduced 4 transcription factors:
Oct4, Sox2 → Activate Nanog (stemness).
c-Myc → Opens chromatin for reprogramming.
Klf4 → Prevents apoptosis.
iPSCs can then differentiate into various tissues (heart, nerve, etc.).
Major advantage: Avoids ethical concerns of using embryos.
What are organoids and why are they important?
Organoids: 3D miniature versions of organs grown in vitro from stem cells.
Created from either:
iPSCs (induced pluripotent stem cells) or
ESCs (embryonic stem cells).
Advantages:
Model normal organ development.
Study diseases using patient-derived cells.
Maintain in culture for over a year.
Grown in 3D extracellular matrix scaffolds to support tissue-like structure.
How can organoids help investigate congenital birth defects?
Researchers create brain organoids from patient cells (e.g., microcephaly).
Allow observation of:
Developmental abnormalities.
How and when errors occur in brain formation.
How are cerebral organoids used to study brain development?
Cerebral organoids self-organize into:
Neuroepithelium (early brain tissue layer).
Apical-basal polarity (top-bottom organization) allows further brain structure formation.
Cultured in bioreactors to improve oxygen and nutrient flow.
Mimic early development of neural tube and neural stem cell niches.
Valuable for studying human brain diseases and development.
What specific findings were made in microcephaly research using organoids?
In microcephaly patient-derived organoids:
Radial glial cells (important stem cells) failed to divide properly.
Cause: Mutation in mitotic spindle proteins (affects accurate cell division).
Result: Reduced brain size (hallmark of microcephaly).
What are the future applications of iPSC technology in medicine?
Patient’s own cells can be:
Reprogrammed to iPSCs.
Genetically corrected (e.g., using CRISPR/Cas9).
Differentiated into healthy tissue and transplanted back into the patient.
Drug screening: Test patient-specific treatments on iPSC-derived tissues.
Goal: Personalized, autologous (self-derived) regenerative therapies without immune rejection.
What are the two main sources of pluripotent stem cells?
Blastocysts: Provide embryonic stem cells (from Inner Cell Mass).
Adult somatic cells: Can be reprogrammed into iPSCs.
Importance: Both sources can generate cells for studying development, disease, and therapy, but iPSCs avoid many ethical issues.
What concerns exist around commercial stem cell clinics?
Many unregulated clinics offer unproven stem cell treatments.
Only FDA-approved and TGA-approved stem cell therapy:
Hematopoietic Stem Cell Transplantation (for blood cancers, immune disorders).
Risks of unproven therapies:
Infection.
Allergic reactions.
Development of tumors (cancer).
Patients should be cautious and seek treatments only from verified clinical trials or approved centers.
